Quasars and Other Active GalaxiesQuasars and Other Active GalaxiesQuasars and Other Active GalaxiesQuasars and Other Active Galaxies
Active galaxies are brighter, and emit more non-stellar radiation
In this chapter you will discover… 5-10% of galaxies unusually bright, called active galaxies
The most distant objects we can see: quasars
Supermassive black holes are central engines for radio galaxies, quasars, Seyfert galaxies, & BL Lac objects
Distribution of Quasars is a key to the evolution of the Universe, and to the Big Bang Theory of its formation.
Active Galaxy TypesActive Galaxy Types
Seyfert GalaxiesSeyfert Galaxies: : Spirals with very bright centersSpirals with very bright centers
Radio GalaxiesRadio Galaxies: : Ellipticals with huge emissions of Ellipticals with huge emissions of radio energy in “lobes”radio energy in “lobes”
Quasars:Quasars: Very tiny, distant objectsVery tiny, distant objects
All have very bright, All have very bright, active galactic nucleiiactive galactic nucleii
Active Galactic NucleiActive Galactic Nuclei
• Seyfert GalaxiesSeyfert Galaxies
• spiral galaxies with spiral galaxies with incredibly bright, star-incredibly bright, star-like center (nucleus)like center (nucleus)
• they are very bright in they are very bright in the infraredthe infrared
• their spectra show their spectra show strong strong emissionemission lines lines
Circinus
Active Galactic NucleiActive Galactic Nuclei
• Seyfert GalaxiesSeyfert Galaxies
The luminosity can vary by as much as the entire brightness of the Milky Way Galaxy!!
Radio Galaxies
Cygnus A Radio Image
635 Million light years away, and still one of the brightest radio sources in the entire sky!
Active Galactic NucleiActive Galactic Nuclei Radio GalaxiesRadio Galaxies
||galaxies – usually giant galaxies – usually giant ellipticalsellipticals - which emit large amounts of radio waves - which emit large amounts of radio waves
the radio emission come from the radio emission come from lobeslobes on either side of the galaxy; on either side of the galaxy; notnot the the galaxy itselfgalaxy itself
Radio Galaxy LobesRadio Galaxy LobesThese lobes are swept back because the galaxy is moving through an intergalactic medium.
X-ray/Radio Image of Centaurus AX-ray/Radio Image of Centaurus A
X-ray is blue; radio is red
BL-Lac Objects
Superbright Elliptical Galaxy
Quasars
A peculiar Star-like object, emitting lots of radio waves? But not with a stellar spectral fingerprint!
Quasar SpectraQuasar Spectra
Star-like objectsStar-like objectsspectra that look spectra that look
nothing like a starnothing like a starFaint Hydrogen Faint Hydrogen
lines…lines…VERY red-shifted!VERY red-shifted!
Quasar ObservationsQuasar Observations
emit light at all wavelengthsemit light at all wavelengthsA hot dense source?A hot dense source?
occasionally VERY strong radio sourcesoccasionally VERY strong radio sourcesAssociated with jets from galaxies in clustersAssociated with jets from galaxies in clusters
Quasars Brightness varies in time!
Quasars Brightness varies in time!
QuasarsQuasars
Show enormous Show enormous redshiftsredshifts VERY far VERY far away by Hubble’s Lawaway by Hubble’s Law
Show extreme Show extreme variabilityvariability VERY small, VERY small, in scales of a light-hours to light years in scales of a light-hours to light years
….and so….….and so….
Quasars must be some of the most powerful Quasars must be some of the most powerful objects we know of in the universe!objects we know of in the universe!
Quasar DistributionQuasar Distribution
Seen at greatest distances Seen at greatest distances (earliest history of the universe!)(earliest history of the universe!)
Not seen nearby…. Not seen nearby….
But…But…
Quasar behavior in some nearer Quasar behavior in some nearer clustersclusters
AA theoretical model quasartheoretical model quasar
Must account for observations:Must account for observations:Small SizeSmall SizeEnormous energyEnormous energy output across spectrum output across spectrumSource of JetsSource of JetsSimilar behavior in Similar behavior in galaxies in clustersgalaxies in clustersSome radio synchrotron emission (indicating Some radio synchrotron emission (indicating
magnetic field)magnetic field)Full spectrumFull spectrum emission emission
A quasar model…A quasar model…
Supermassive Black Hole EngineSupermassive Black Hole Engine
Formed as Galaxies are born…Formed as Galaxies are born…
Pulling in gas, dust, and stars into huge Pulling in gas, dust, and stars into huge accretion diskaccretion disk
A quasar model…A quasar model…
Generating Generating jets of X-ray radiationjets of X-ray radiation for for millions of yearsmillions of years
““Quiet down” as fuel diminishesQuiet down” as fuel diminishes
““Re-ignited”Re-ignited” during collisions & mergers of during collisions & mergers of galaxies in clustersgalaxies in clusters
Quasar Energy Source?Quasar Energy Source? The energy is generated from matter falling onto The energy is generated from matter falling onto
a a supermassive black holesupermassive black hole…… 1.2 x 101.2 x 1099 M M for NGC 4261 for NGC 4261 3 x 103 x 1099 M M for M87 for M87
……which is at the center (nucleus) of the galaxy.which is at the center (nucleus) of the galaxy.
Quasar Energy Source?Quasar Energy Source?
Matter swirls through an accretion disk Matter swirls through an accretion disk before crossing over the event horizon.before crossing over the event horizon.
Gravitational energy lost like E = mcGravitational energy lost like E = mc22 • 10 – 40% of this is radiated away10 – 40% of this is radiated away
Process is very efficientProcess is very efficient
A quasar model…A quasar model…
Works to explain quasarsWorks to explain quasarsEven Supermassive Black holes are TINYEven Supermassive Black holes are TINYAccretion Disk generates thermal spectrum, Accretion Disk generates thermal spectrum,
jets, magnetic fieldsjets, magnetic fieldsHighly variable as mass is pulled inHighly variable as mass is pulled in
and…and…Works for active galaxies, too!Works for active galaxies, too!
Theory
Observation
Magnetic fields twistedMagnetic fields twisted
Pull charged particles out of disk & Pull charged particles out of disk & accelerate like slingshotaccelerate like slingshot
Particles bound to magnetic field; Particles bound to magnetic field; focused in a beamfocused in a beam
Quasar Jet Formation
Orientation determines what we see:Orientation determines what we see:
• if beams points at us, see a if beams points at us, see a quasarquasar
• if not, molecular clouds/dust of galaxy if not, molecular clouds/dust of galaxy block view of nucleusblock view of nucleus
• we see a radio galaxy or Seyfertwe see a radio galaxy or Seyfert
• lobeslobes are where jets impact are where jets impact intergalactic mediumintergalactic medium
Model Quasar Accounts for Other Observations, too
Hubble space telescope shows us that Hubble space telescope shows us that quasars do live in galaxies…they are quasars do live in galaxies…they are
Active Galactic Nuclei!Active Galactic Nuclei!
If the theory is right --- all galaxies start with Black Holes!
Evidence Quasars are distant?Evidence Quasars are distant?
Hubble’s LawHubble’s LawAssociation with Galaxies in clustersAssociation with Galaxies in clustersGravitational LensingGravitational Lensing
Essay Questions to Know!Essay Questions to Know!
What are active galaxies? How do active galaxies produce their energy? How do we know?
What are quasars, and where are they found? What do they tell us about the universe?